The present invention is directed to polycarbonate sizing compositions and method of application thereof.
Various types of fibers such as carbon fibers have been employed as reinforcement in composite structures for some time. In an attempt to enhance the physical characteristics of such fibers as reinforcing agents, the fibers have been coated or sized with various compounds such as polycarbonates.
Typically, such polycarbonate sizing finishes are applied to the fiber from a sizing bath comprised of the polycarbonate dissolved in a methylene chloride solvent. A concentration of polycarbonate on the order of about 6 percent by weight is generally employed in such baths in an attempt to provide a finished fiber having a concentration of about 2 percent by weight of polycarbonate thereon. However, since methylene chloride evaporates very readily, it is difficult to maintain a substantially constant polycarbonate concentration in the bath during the sizing operation. As a result, the polycarbonate concentration on the finished fiber tends to vary significantly during the sizing operation.
As an alternative to the use of methylene chloride as a sizing solvent, it has been suggested that N-methyl-2-pyrrolidone (NMP) be employed. While NMP is a suitable solvent for polycarbonates, the solvent is not easily removed from the finished fiber. However, it is desirable to remove substantially all of the solvent from the fiber to avoid undesirably modifying the physical characteristics of the fiber as well as to prevent interference with the composite performance at the fiber-matrix interface.